The present invention relates, in general, to semiconductor devices and more particularly, to silicon carbide semiconductor devices.
The semiconductor industry has utilized a variety of processes and structures to form metal semiconductor field effect transistors (MESFETs) from silicon carbide. One problem with these prior transistors is the inability to form structures having a gate that is self-aligned to source and drain areas of the transistor. Activation of dopants within silicon carbide usually requires heating the silicon carbide and the dopants to temperatures in excess of 1200.degree. C. Such high temperatures are detrimental to the materials typically utilized to form the gate of the MESFET. The high temperatures result in destroying the junction formed at the interface of the gate material and the channel, and can also result in significantly deforming the shape of the gate.
Consequently, prior silicon carbide MESFETs generally form source and drain implants, and activate the implants prior to depositing the gate. As a result, the gate is not self-aligned to the source and drain areas. Consequently, the gate to source spacing is larger than that which can be obtained from a self-aligned transistor, and the resulting transconductance and frequency response is less than that which can be obtained from a self-aligned transistor.
Accordingly, it is desirable to have a silicon carbide MESFET having a gate that is self-aligned to the source, that is self-aligned to the drain, and that has a gate-to-source spacing of less than 0.5 microns.